Follow-up of bug 188043. This might need a bit more work so I'm moving that part out of the main bug.
Basically, the patch in bug 188043 naively follows https://drafts.csswg.org/cssom-view/#scroll-an-element-into-view but does not wait for smooth scroll of step 12 to complete, possibly resulting in wrong final positions. It's not clear we actually want to align on the current spec anyway, Gecko and Chromium use different algorithm. For details, see https://github.com/w3c/csswg-drafts/issues/3127
The WPT test for this is http://w3c-test.org/css/cssom-view/scroll-behavior-scrollintoview-nested.html